Reexamination of Fat Globule Clustering and Creaming in Cow Milk

Abstract

Fat globule clustering, as characterized by cream volume and cluster time, was studied in raw milk, heated milk, homogenized milk, and in model systems. Immunoglobulin M was confirmed as the heat-labile component in fat globule clustering and was shown to function as a cryoagglutinin rather than as a cryoglobulin as previously indicated. Hapten inhibition studies demonstrated that the antigen is carbohydrate. Skim milk membrane was identified as the homogenization-labile component. Although immunoglobulin M can agglutinate milk fat globules to a limited extent, normal creaming requires both immunoglobulin M and skim milk membrane. Approximately 7% of the immunoglobulin M in normal milk participates in a single creaming. The lower portion of creamed milk (gravity separated skim milk) failed to support creaming on addition of washed fat globules but did so on addition of skim milk membrane. A theory of fat globule clustering consistent with observed experimental results depicts immunoglobulin M interacting in an antigenantibody mode simultaneously with skim milk membrane and milk fat globules through specific carbohydrate moieties.